Oxygen-18 Content of Atmospheric Oxygen Does Not Affect the Oxygen Isotope Relationship between Environmental Water and Cellulose in a Submerged Aquatic Plant, Egeria densa Planch

We determined that the oxygen isotopic composition of cellulose synthesized by a submerged plant, Egeria densa Planch., is related to the isotopic composition of environmental water by a linear function, δ¹⁸O cellulose = 0.48 δ¹⁸O water + 24.1%‰. The observation of a slope of less than 1 indicates that a portion of cellulose oxygen is derived from an isotopically constant source other than water. We tested whether this source might be molecular oxygen by growing plants in the presence of high concentrations of ¹⁸O in the form of O₂ bubbled into the bottom of an aquarium. Cellulose synthesized during this experiment did not have significantly different oxygen isotope ratios than that synthesized by control plants exposed to O₂ of normal ¹⁸O abundance. We propose that oxygen in organic matter recycled from senescent portions of the plant is incorporated into cellulose. Our findings indicate that paleoclimatic models linking the oxygen isotope composition of environmental water to cellulose from fossil plants will have to be modified to account for contributions of oxygen from this or other sources besides water.     

Stable Hydrogen Isotope Fractionations during Autotrophic and Mixotrophic Growth of Microalgae

Isotope effects, studied with precision isotope ratio mass spectrometry, have been used to locate critical steps in the H metabolism of plants. By manipulating the growth conditions of versatile microalgae, the discrimination of H isotopes between water in the growth medium and the organically bonded H in carbohydrates from these microalgae was −100 to −120‰ and was regulated by both the light and the dark reactions of photosynthesis. Photosynthetic electron transport discriminated against the heavy isotope of H and formed a pool of reductant available for biosynthesis that was enriched in the light isotope. Growth in red or white light activated phosphoglyceric acid reduction and H isotope discrimination, when H was fixed into organic matter. An additional fractionation of −30 to −60‰ occurred during the biosynthesis of proteins and lipids and was associated with glycolysis. This fractionation paralleled the isotope effect seen in carbohydrate metabolism, indicating that H metabolism in photosynthesis was coupled with that in dark biosynthetic reactions via the pool of reductant, probably NADPH.     

Endogenous NO levels regulate nodule functioning: Potential role of cGMP in nodule functioning?

Nitric oxide is a small gaseous signaling molecule which functions in the regulation of plant development and responses to biotic and abiotic stresses. Recently, we have shown that nitric oxide is required for development of functional nodules. Here, we show that inhibition of nitric oxide synthase enzymatic activity (using N_ω-nitro-L-arginine) reduces nitric oxide content in soybean root nodules and this is coupled by reduction of endogenous cyclic guanosine monophosphate content in the nodules. We postulate that the regulation of soybean nodule development by nitric oxide is transduced via cyclic guanosine monophosphate through activation of nitric oxide-responsive soluble guanylate cyclase. Furthermore, we hypothesize that this signaling cascade is mediated via modulation of the activities of antioxidant metabolic pathways.Key words: cyclic guanosine monophosphate, nitric oxide synthase, nitric oxide, nitrogen fixation, nodulation efficiency, nodule functioning, reactive oxygen species     

Isotope Fractionation in Photosynthetic Bacteria during Carbon Dioxide Assimilation

The δ _PDB¹³C values have been determined for the cellular constituents and metabolic intermediates of autotrophically grown Chromatium vinosum. The isotopic composition of the HCO₃^- in the medium and the carbon isotopic composition of the bacterial cells change with the growth of the culture. The δ _PDB¹³C value of the HCO₃^- in the media changes from an initial value of −6.6‰ to +8.1‰ after 10 days of bacterial growth and the δ _PDB¹³C value of the bacterial cells change from −37.5‰ to −29.2‰ in the same period. The amount of carbon isotope fractionation during the synthesis of hexoses by the photoassimilation of CO₂ has a range of −15.5‰ at time zero to −22.0‰ after 10 days. This range of fractionation compares to the range of carbon isotope fractionation for the synthesis of sugars from CO₂ by ribulose 1,5-diphosphate carboxylase and the Calvin cycle.     

34S/32S and 18O/16O Fractionation During Sulfur Disproportionation by Desulfobulbus propionicus

In the present study, coupled stable sulfur and oxygen isotope fractionation during elemental sulfur disproportionation according to the overall reaction: 4H₂O + 4S^? → 3H₂S + SO₄ ^{2 ?} + 2H⁺, was experimentally investigated for the first time using a pure culture of the sulfate reducer Desulfobulbus propionicus at 35^?C. Bacterial disproportionation of elemental sulfur is an important process in the sulfur cycle of natural surface sediments and leads to the simultaneous formation of sulfide and sulfate. A dual-isotope approach considering both sulfur and oxygen isotope discrimination has been shown to be most effective in evaluating specific microbial reactions. The influence of iron- and manganese bearing-solids (Fe(II)CO₃, Fe(III)OOH, Mn(IV)O₂) acting in natural sediments as scavengers for hydrogen sulfide, was considered, too. Disproportionation of elemental sulfur was observed in the presence of iron solids at a cell-specific sulfur disproportionation rate of about 10^{? 9.5± 0.4} μ mol S^? cell^{? 1} h^{? 1}. No disproportionation, however, was observed with MnO₂. In the presence of iron solids, newly formed sulfate was enriched in ¹⁸ O compared to water by about +21‰ (≡ ? _H2O ), in agreement with a suggested oxygen isotope exchange via traces of intra- or extracellular sulfite that is formed as a disproportionation intermediate. Dissolved sulfate was also enriched in ³⁴S compared to elemental sulfur by up to +35%. Isotope fractionation by Desulfobulbus propionicusis highest for all disproportionating bacteria investigated, so far, and may impact on the development of isotope signals at the redox boundary of surface sediments.     

Carbon isotope fractionation by ribulose-1,5-bisophosphate carboxylase from various organisms

Carbon isotope fractionation by structurally and catalytically distinct ribulose-1,5-bisphosphate carboxylases from one eucaryotic and four procaryotic organisms has been measured under nitrogen. The average fractionation for 40 experiments was −34.1 ‰ with respect to the δ¹³C of the dissolved CO₂ used, although average fractionations for each enzyme varied slightly: spinach carboxylase, −36.5 ‰; Hydrogenomonas eutropha, −38.7 ‰; Agmenellum quadruplicatum, −32.2 ‰; Rhodospirillum rubrum, −32.1 ‰; Rhodopseudomonas sphaeroides peak I carboxylase, −31.4 ‰; and R. sphaeroides peak II carboxylase, −28.3 ‰. The carbon isotope fractionation value was largely independent of method of enzyme preparation, purity, or reaction temperature, but in the case of spinach ribulose-1,5-bisphosphate carboxylase fractionation, changing the metal cofactor used for enzyme activation had a distinct effect on the fractionation value. The fractionation value of −36.5 ‰ with Mg²⁺ as activator shifted to −29.9 ‰ with Ni²⁺ as activator and to −41.7 ‰ with Mn²⁺ as activator. These dramatic metal effects on carbon isotope fractionation may be useful in examining the catalytic site of the enzyme.     

Diversity of Sulfur Isotope Fractionations by Sulfate-Reducing Prokaryotes

Batch culture experiments were performed with 32 different sulfate-reducing prokaryotes to explore the diversity in sulfur isotope fractionation during dissimilatory sulfate reduction by pure cultures. The selected strains reflect the phylogenetic and physiologic diversity of presently known sulfate reducers and cover a broad range of natural marine and freshwater habitats. Experimental conditions were designed to achieve optimum growth conditions with respect to electron donors, salinity, temperature, and pH. Under these optimized conditions, experimental fractionation factors ranged from 2.0 to 42.0‰. Salinity, incubation temperature, pH, and phylogeny had no systematic effect on the sulfur isotope fractionation. There was no correlation between isotope fractionation and sulfate reduction rate. The type of dissimilatory bisulfite reductase also had no effect on fractionation. Sulfate reducers that oxidized the carbon source completely to CO₂ showed greater fractionations than sulfate reducers that released acetate as the final product of carbon oxidation. Different metabolic pathways and variable regulation of sulfate transport across the cell membrane all potentially affect isotope fractionation. Previous models that explained fractionation only in terms of sulfate reduction rates appear to be oversimplified. The species-specific physiology of each sulfate reducer thus needs to be taken into account to understand the regulation of sulfur isotope fractionation during dissimilatory sulfate reduction.     

Salinity Responses of Benthic Microbial Communities in a Solar Saltern (Eilat, Israel)

The salinity responses of cyanobacteria, anoxygenic phototrophs, sulfate reducers, and methanogens from the laminated endoevaporitic community in the solar salterns of Eilat, Israel, were studied in situ with oxygen microelectrodes and in the laboratory in slurries. The optimum salinity for the sulfate reduction rate in sediment slurries was between 100 and 120‰, and sulfate reduction was strongly inhibited at an in situ salinity of 215‰. Nevertheless, sulfate reduction was an important respiratory process in the crust, and reoxidation of formed sulfide accounted for a major part of the oxygen budget. Methanogens were well adapted to the in situ salinity but contributed little to the anaerobic mineralization in the crust. In slurries with a salinity of 180‰ or less, methanogens were inhibited by increased activity of sulfate-reducing bacteria. Unicellular and filamentous cyanobacteria metabolized at near-optimum rates at the in situ salinity, whereas the optimum salinity for anoxygenic phototrophs was between 100 and 120‰.     

Crystal morphology and carbon/carbon composition of solid oxalate in cacti

Morphology, crystal structure, and carbon isotopic composition of calcium oxalate from representative species from the family Cactaceae were determined using scanning electron microscopy, x-ray diffraction, and isotope ratio mass spectrometry. Crystals from one species in the Opuntieae tribe of the Cactaceae were druses with acute points composed of the monohydrate form of calcium oxalate (whewellite). Crystals from three species in the Cereeae tribe were the dihydrate form of calcium oxalate (weddellite) forming druses made up of tetragonal and isodiametric crystallites. The oxalate was relatively enriched in ¹³C isotope (-7.3 to - 8.7 ‰) compared with woody fibers (-13.3 to 14.1 ‰) from the same plants.     

Temperature Dependence of Carbon Isotope Fractionation in CAM Plants

The carbon isotope fractionation associated with nocturnal malic acid synthesis in Kalanchoë daigremontiana and Bryophyllum tubiflorum was calculated from the isotopic composition of carbon-4 of malic acid, after appropriate corrections. In the lowest temperature treatment (17°C nights, 23°C days), the isotope fractionation for both plants is −4‰ (that is, malate is enriched in ¹³C relative to the atmosphere). For K. daigremontiana, the isotope fractionation decreases with increasing temperature, becoming approximately 0‰ at 27°C/33°C. Detailed analysis of temperature effects on the isotope fractionation indicates that stomatal aperture decreases with increasing temperature and carboxylation capacity increases. For B. tubiflorum, the temperature dependence of the isotope fractionation is smaller and is principally attributed to the normal temperature dependences of the rates of diffusion and carboxylation steps. The small change in the isotopic composition of remaining malic acid in both species which is observed during deacidification indicates that malate release, rather than decarboxylation, is rate limiting in the deacidification process.     

Environmental context for the terminal Ediacaran biomineralization of animals

In terminal Ediacaran strata of South China, the onset of calcareous biomineralization is preserved in the paleontological transition from Conotubus to Cloudina in repetitious limestone facies of the Dengying Formation. Both fossils have similar size, funnel‐in‐funnel construction, and epibenthic lifestyle, but Cloudina is biomineralized, whereas Conotubus is not. To provide environmental context for this evolutionary milestone, we conducted a high‐resolution elemental and stable isotope study of the richly fossiliferous Gaojiashan Member. Coincident with the first appearance of Cloudina is a significant positive carbonate carbon isotope excursion (up to +6‰) and an increase in the abundance and ³⁴S composition of pyrite. In contrast, δ³⁴S values of carbonate‐associated sulfate remain steady throughout the succession, resulting in anomalously large (>70‰) sulfur isotope fractionations in the lower half of the member. The fractionation trend likely relates to changes in microbial communities, with sulfur disproportionation involved in the lower interval, whereas microbial sulfate reduction was the principal metabolic pathway in the upper. We speculate that the coupled paleontological and biogeochemical anomalies may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin, which stimulated primary productivity, the spread of an oxygen minimum zone, and the development of euxinic conditions in subtidal and basinal environments. Enhanced production and burial of organic matter is thus directly connected to the carbon isotope anomaly, and likely promoted pyritization as the main taphonomic pathway for Conotubus and other soft‐bodied Ediacara biotas. Our studies suggest that the Ediacaran confluence of ecological pressures from predation and environmental pressures from an increase in seawater alkalinity set the stage for an unprecedented geobiological response: the evolutionary novelty of animal biomineralization.     

Chaetognatha of the Namibian Upwelling Region: Taxonomy,Distribution and Trophic Position

In October 2010, the vertical distribution, biodiversity and maturity stages of Chaetognatha species were investigated at four stations located off Walvis Bay, Namibia. Seventeen species were detected and classified as pelagic, shallow-mesopelagic, deep-mesopelagic and bathypelagic species based upon the weighted mean depth derived from their average vertical distribution. High abundances of Chaetognatha were found in the upper 100 m at all stations of the Walvis Bay transect with a maximum value of 20837 ind. 1000 m⁻³ at the outer shelf station near the surface. The community was dominated by species of the Serratodentata group. Furthermore, the distribution of Chaetognatha did not seem to be influenced by low oxygen concentrations. Stable isotope ratios of carbon and nitrogen in Chaetognatha were determined for seven different areas located off northern Namibia. The values of δ¹⁵N ranged from 6.05 ‰ to 11.39 ‰, while the δ¹³C values varied between −23.89 ‰ and −17.03 ‰. The highest values for δ¹⁵N were observed at the Walvis Bay shelf break station. The lowest δ¹³C values were found at the Rocky Point offshore station, which was statistically different from all other areas. Stable isotopes of carbon and nitrogen were determined for four taxa (Sagitta minima, Planctonis group, Sagitta enflata, Sagitta decipiens). In this case, the δ¹⁵N values ranged from 6.17 ‰ to 10.38 ‰, whereas the δ¹³C values varied from −22.70 ‰ to −21.56 ‰. The lowest δ¹⁵N values were found for S. minima. The C- and N-content revealed maximum C-values for S. decipiens and maximum N-values for the Planctonis group. The C:N ratio of Chaetognatha ranged between 5.25 and 6.20. Overall, Chaetognatha are a diverse group in the pelagic food web of the Benguela Upwelling System and act as competitors of fish larvae and jelly fish by preying on copepods.     

Carbon isotope ratios demonstrate carbon flux from c(4) host to c(3) parasite

Carbon isotope ratios of mature leaves from the C₃ angiosperm root hemiparasites Striga hermonthica (Del.) Benth (−26.7‰) and S. asiatica (L.) Kuntze (−25.6‰) were more negative than their C₄ host, sorghum (Sorghum bicolor [L.] Moench cv CSH1), (−13.5‰). However, in young photosynthetically incompetent plants of S. hermonthica this difference was reduced to less than 1‰. Differences between the carbon isotope ratios of two C₃-C₃ associations, S. gesnerioides (Willd.) Vatke—Vigna unguiculata (L.) Walp. and Oryza sativa L.—Rhamphicarpa fistulosa (Hochst.) Benth differed by less than 1‰. Theoretical carbon isotope ratios for mature leaves of S. hermonthica and S. asiatica, calculated from foliar gas exchange measurements, were −31.8 and −32.0‰, respectively. This difference between the measured and theoretical δ¹³C-values of 5 to 6‰ suggests that even in mature, photosynthetically active plants, there is substantial input of carbon from the C₄ host. We estimate this to be approximately 28% of the total carbon in S. hermonthica and 35% in S. asiatica. This level of carbon transfer contributes to the host's growth reductions observed in Striga-infected sorghum.     

Nitrogen fixation and respiration by root nodules ofAlnus rubra Bong.: Effects of temperature and oxygen concentration

Summary Using a root nodule cuvette and a continuous flow gas exchange system, we simultaneously measured the rates of carbon dioxide evolution, oxygen uptake and acetylene reduction by nodules ofAlnus rubra. This system allowed us to measure the respiration rates of single nodules and to determine the effects of oxygen concentration and temperature on the energy cost of nitrogen fixation. Energy cost was virtually unchanged (2.8–3.5 moles of carbon dioxide or oxygen per mole of ethylene) from 16 to 26°C (pO₂=20 kPa) while respiration and nitrogenase activity were highly temperature dependent. At temperatures below 16°C, nitrogenase activity decreased more than did respiration and as a result, energy cost rose sharply. Acetylene reduction ceased below 8°C. Inhibition of nitrogenase activity at low temperatures was rapidly reversed upon return to higher temperatures. At high temperatures (above 30°C) nitrogenase activity declined irreversibly, while respiration and energy cost increased.Energy cost was nearly unchanged at oxygen partial pressures of 5 to 20 kPa (temperature of 20°C). Respiration and nitrogenase activity were strongly correlated with oxygen tension. Below 5 kPa, acetylene reduction and oxygen uptake decreased sharply while production of carbon dioxide increased, indicating fermentation. Fermentation alone was unable to support nitrogenase activity. Acetylene reduction was independent of oxygen concentration from 15 to 30 kPa. Nitrogenase activity decreased and energy cost rose above 30 kPa until nearly complete inactivation of nitrogenase at 70–80 kPa. Activity declined gradually, such that acetylene reduction at a constant oxygen concentration was stable, but showed further inactivation when oxygen concentration was once again increased. Alder nodules appear to consist of a large number of compartments that differ in the degree to which nitrogenase is protected from excess oxygen.Supported by United States Department of Agriculture Grant 78-59-2252-0-1-005-1     

Biogeochemical Signals from Deep Microbial Life in Terrestrial Crust

In contrast to the deep subseafloor biosphere, a volumetrically vast and stable habitat for microbial life in the terrestrial crust remains poorly explored. For the long-term sustainability of a crustal biome, high-energy fluxes derived from hydrothermal circulation and water radiolysis in uranium-enriched rocks are seemingly essential. However, the crustal habitability depending on a low supply of energy is unknown. We present multi-isotopic evidence of microbially mediated sulfate reduction in a granitic aquifer, a representative of the terrestrial crust habitat. Deep meteoric groundwater was collected from underground boreholes drilled into Cretaceous Toki granite (central Japan). A large sulfur isotopic fractionation of 20–60‰ diagnostic to microbial sulfate reduction is associated with the investigated groundwater containing sulfate below 0.2 mM. In contrast, a small carbon isotopic fractionation (<30‰) is not indicative of methanogenesis. Except for 2011, the concentrations of H₂ ranged mostly from 1 to 5 nM, which is also consistent with an aquifer where a terminal electron accepting process is dominantly controlled by ongoing sulfate reduction. High isotopic ratios of mantle-derived ³He relative to radiogenic ⁴He in groundwater and the flux of H₂ along adjacent faults suggest that, in addition to low concentrations of organic matter (<70 µM), H₂ from deeper sources might partly fuel metabolic activities. Our results demonstrate that the deep biosphere in the terrestrial crust is metabolically active and playing a crucial role in the formation of reducing groundwater even under low-energy fluxes.     

Effect of water stress on the reduction of nitrate and nitrite by soybean nodules

The effects of water stress on nitrate reductase and nitrite reductase activities in symbiotic nodules were examined in field-grown soybean plants (Glycine max L Merr. cv Clark). The in vitro assays of enzyme activity indicated that the nodule cytosol and bacteroids contained both nitrate reductase and nitrite reductase activities. The reduction of nitrate in bacteroids increased significantly as nodule water potential declined from −0.6 to −1.4 megapascals, and then decreased when −1.8 megapascals water potential was reached. On the contrary, the reduction of nitrate in nodule cytosol was inhibited as water stress progressed. Increases in water stress intensity also caused a significant inhibition in nitrite reductase activities of bacteroids and nodule cytosol within soybean nodules. The results show that nitrate reduction occurred both in the cytosol and bacteroids of water-stressed soybean nodules. The reduction of nitrate functioned at different physiological modes in these two fractions.     

Isotopic Incorporation Rates and Discrimination Factors in Mantis Shrimp Crustaceans

Stable isotope analysis has provided insights into the trophic ecology of a wide diversity of animals. Knowledge about isotopic incorporation rates and isotopic discrimination between the consumer and its diet for different tissue types is essential for interpreting stable isotope data, but these parameters remain understudied in many animal taxa and particularly in aquatic invertebrates. We performed a 292-day diet shift experiment on 92 individuals of the predatory mantis shrimp, Neogonodactylus bredini, to quantify carbon and nitrogen incorporation rates and isotope discrimination factors in muscle and hemolymph tissues. Average isotopic discrimination factors between mantis shrimp muscle and the new diet were 3.0 ± 0.6 ‰ and 0.9 ± 0.3 ‰ for carbon and nitrogen, respectively, which is contrary to what is seen in many other animals (e.g. C and N discrimination is generally 0–1 ‰ and 3–4 ‰, respectively). Surprisingly, the average residence time of nitrogen in hemolymph (28.9 ± 8.3 days) was over 8 times longer than that of carbon (3.4 ± 1.4 days). In muscle, the average residence times of carbon and nitrogen were of the same magnitude (89.3 ± 44.4 and 72.8 ± 18.8 days, respectively). We compared the mantis shrimps’ incorporation rates, along with rates from four other invertebrate taxa from the literature, to those predicted by an allometric equation relating carbon incorporation rate to body mass that was developed for teleost fishes and sharks. The rate of carbon incorporation into muscle was consistent with rates predicted by this equation. Our findings provide new insight into isotopic discrimination factors and incorporation rates in invertebrates with the former showing a different trend than what is commonly observed in other animals.     

Regulation of soybean nitrogen fixation in response to rhizosphere oxygen: I. Role of nodule respiration

Nitrogen fixation (acetylene reduction) rates of nodules on intact field-grown soybean (Glycine max) subjected to altered oxygen concentration (0.06-0.4 cubic millimeter per cubic millimeter) returned to initial rates during an 8-hour transitory period. Hydroponically grown soybean plants also displayed a transitory (1-4 hours) response to changes in the rhizosphere oxygen concentration after which the fixation rates returned to those observed under ambient oxygen concentrations. It was hypothesized that soybean nodules contain a regulatory mechanism which maintains a stable oxygen concentration inside nodules at a sufficiently low concentration to allow nitrogenase to function. A possible physiological mechanism which could account for this regulation is adjustment in nodule respiration activity such that nodule oxygen concentration and nitrogen fixation are maintained at stable levels. Experiments designed to characterize the non-steady-state oxygen response and to test for the presence of nodule respiratory control are presented. Non-steady-state acetylene reduction and nodule respiration (oxygen uptake) rates measured after alterations in the external oxygen concentration indicated that the regulatory mechanism required 1 to 4 hours to completely adjust to changes in the external oxygen concentration. Steady-state nodule respiration, however, did not respond to alterations in the rhizosphere oxygen concentration. It was concluded that soybean nodules can adjust to a wide range of rhizosphere oxygen concentrations, but the mechanism which controls nitrogen fixation rates does not involve changes in the nodule respiration rate.     

Effect of Varying CO(2) Partial Pressure on Photosynthesis and on Carbon Isotope Composition of Carbon-4 of Malate from the Crassulacean Acid Metabolism Plant Kalanchoë daigremontiana Hamet et Perr

Intact leaves of Kalanchoë daigremontiana were exposed to CO₂ partial pressures of 100, 300, and 1000 microbars. Malic acid was extracted, purified, and degraded in order to obtain isotopic composition of carbon-1 and carbon-4. From these data, it is possible to calculate the carbon isotope composition of newly fixed carbon in malate. In all three treatments, the isotopic composition of newly introduced carbon is the same as that of the CO₂ source and is independent of CO₂ partial pressures over the range tested. Comparison with numerical models described previously (O'Leary 1981 Phytochemistry 20: 553-567) indicates that we would expect carbon 4 of malate to be 4‰ more negative than source CO₂ if diffusion is totally limiting or 7‰ more positive than source CO₂ if carboxylation is totally limiting. Our results demonstrate that stomatal aperture adjusts to changing CO₂ partial pressures and maintains the ratio of diffusion resistance to carboxylation resistance approximately constant. In this study, carboxylation and diffusion resistances balance so that essentially no fractionation occurs during malate synthesis. Gas exchange studies of the same leaves from which malate was extracted show that the extent of malate synthesis over the whole night is nearly independent of CO₂ partial pressure, although there are small variations in CO₂ uptake rate. Both the gas exchange and the isotope studies indicate that the ratio of external to internal CO₂ partial pressure is the same in all three treatments. Inasmuch as a constant ratio will result in constant isotope fractionation, this observation may explain why plants in general have fairly invariable ¹³C contents, despite growing under a variety of environmental conditions.     

Exploring the Potential of Laser Ablation Carbon Isotope Analysis for Examining Ecology during the Ontogeny of Middle Pleistocene Hominins from Sima de los Huesos (Northern Spain)

Laser ablation of tooth enamel was used to analyze stable carbon isotope compositions of teeth of hominins, red deer, and bears from middle Pleistocene sites in the Sierra de Atapuerca in northern Spain, to investigate the possibility that this technique could be used as an additional tool to identify periods of physiological change that are not detectable as changes in tooth morphology. Most of the specimens were found to have minimal intra-tooth variation in carbon isotopes (< 2.3‰), suggesting isotopically uniform diets through time and revealing no obvious periods of physiological change. However, one of the two sampled hominin teeth displayed a temporal carbon isotope shift (3.2‰) that was significantly greater than observed for co-occurring specimens. The δ¹³C value of this individual averaged about -16‰ early in life, and -13‰ later in life. This isotopic change occurred on the canine crown about 4.2 mm from the root, which corresponds to an approximate age of two to four years old in modern humans. Our dataset is perforce small owing to the precious nature of hominid teeth, but it demonstrates the potential utility of the intra-tooth isotope profile method for extracting ontogenetic histories of human ancestors.